Krotty is using a crescent kick to knock the knife out of the attacker's hand - and for advanced students, following with a same-leg side kick to the throat to finish him off.

I don't know what rinky dink dojo you went too, I'm talking about using that cresent kick to knock the knife out and then spining and jumping in t3h d3adly "Tornado" kick to knock them out. The yellow belts let out a collective Ouuusssssaaaaa.